typedef struct Symbol_s { /* Symbol table entry */
	char*	ptr_cname;	/* Symbol Name */
	short	itype;		/* Symbol Type: VAR, BLTIN, UNDEF */
	union {								/* Symbol Value */
		double	dval;					/* if VAR */
		double	(*ptr_dfunc)(double);	/* if BLTIN */
	} u;
	struct Symbol_s* ptr_next;	/* Link to next symbol */
} Symbol_t;

Symbol_t* install(const char *, int, double);
Symbol_t* lookup(const char *);
